GRB 260326A — All Circulars

Xing-Hao Luo, Chen-Wei Wang, Chao Zheng, Cheng-Kui Li and Shao-Lin Xiong (IHEP) report on behalf of the Insight-HXMT team:

At 2026-03-26T01:18:33.250 (T0), Insight-HXMT/HE detected the burst GRB 260326A, which is also detected by Fermi/GBM (Fermi GBM team, GCN #44115).
	
The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 15 +1/-0.5 s. The 1s peak rate, measured from T0+0.75 s, is 6592 cnts/sec. Insight-HXMT/HE detected a total of 39437 counts from this burst.

The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb260326A.png

All measurements above are made with the CsI detectors of Insight-HXMT/HE operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.

Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://hxmten.ihep.ac.cn/

Longhao Li, Xiangyi Wang, Chenyu Wang, Zirui Yang report on behalf of the GRID Collaboration:
GRID-11B reports the detection of the long-duration GRB 260326A, which was also detected by Fermi-GBM (Fermi GBM team, GCN 44115; Pathak & Bala, GCN 44118).
The event was triggered with GRID-11B on 2026-03-26 at 01:18:28 UTC. The measured burst duration (T90) in the 30-2000 keV range is approximately 13.3 +/- 0.6 seconds.
At present, only the GRID light curve is available. No spectral analysis is reported at this stage. The GRID light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260326A/GRID_260326A_ltcv.pdf
GRID is a student-led project to monitor the transient gamma-ray sky with multiple detectors onboard different nanosatellites in the era of multi-messenger astronomy. For more information about GRID, please refer to the following references: https://doi.org/10.1007/s10686-019-09636-w and https://doi.org/10.1007/s10686-021-09819-4.

U. Pathak (IITB) and S. Bala (USRA) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 01:18:28.51 UT on 26 March 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260326A (trigger 796180713/260326054). 
The Fermi GBM real-time Localization is reported in GCN 44115.

The angle from the Fermi LAT boresight is 76 degrees.

The GBM light curve consists of two spikes from a single emission episode with a duration (T90)
of about 50 s (50-300 keV). The time-averaged spectrum
from T0-6.0 to T0+66.0 s is best fit by
a Band function with Epeak = 275 +/- 1 keV,
alpha = -1.040 +/- 0.004, and beta = -2.00 +/- 0.01.

The event fluence (10-1000 keV) in this time interval is
(5.37 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+7.0 s in the 10-1000 keV band is 32.6 +/- 0.4 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

The Fermi GBM team reports the detection of a likely LONG GRB

At 01:18:28 UT on 26 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260326A (trigger 796180713.505606 / 260326054).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 97.9, Dec = 25.4 (J2000 degrees, equivalent to J2000 06h 31m, 25d 23'), with a statistical uncertainty of 1.0 degrees.

The angle from the Fermi LAT boresight is 76.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260326054/quicklook/glg_skymap_all_bn260326054.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260326054/quicklook/glg_healpix_all_bn260326054.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260326054/quicklook/glg_lc_medres34_bn260326054.gif